The invention relates to magnetoresistive recording heads. In particular, the invention relates to a magnetoresistive element-to-contact alignment test structure and method.
A critical parameter in magnetoresistive (MR) recording heads is the alignment between the contacts and the MR elements. Misalignment between the contacts and an MR element causes the MR element's "read center" to shift from its desired position. This in turn causes misalignment between the MR element read center and the write transducer's "write center", thereby decreasing the off-track capabilities of the data head. This is particularly true with respect to MR head designs utilizing slanted contacts and an asymmetric non-rectangular MR element shape. In these MR head designs, misalignment in either of two orthogonal directions causes the read center to shift.
The contacts and MR element layers of an MR head are deposited with the use of photoresist masks or photomasks, which are commonly referred to as reticles. For MR heads there are a number of rows in each reticle. Typically, at the bottom of each reticle is a row of test features which do not become products. The row of test features on each reticle is used for purposes such as determining whether alignment between mask layers is correct, determining film thicknesses, determining completeness of etching, or identifying electrical shorts between layers. In general, analysis of the test features on each reticle is used to determine whether the fabrication process is working properly over the entire wafer.
Because even slight misalignment between MR head mask layers can cause the MR head to function less than optimally, it is necessary to verify alignment of the layers during or after the fabrication process. Visual methods of determining the alignment of reticles from one layer to the next exist. Visual inspection of reticle alignment between layers is a very slow and labor intensive process. Additionally, many of these methods have limited accuracy and leave room for human error. The method of determining alignment accuracy of the present invention is automated and removes the issue of human error due to subjective judgment about the degree of misalignment.